Magnetization and AC permeability measurements show that the shape
memory compounds Co1.52Ni1.32Al1.16 and Co1.8Ni0.92Ga1.28 both order
ferromagnetically below ≈280 K and show a further transition at ≈220 K.
Neutron powder diffraction measurements have confirmed that the lower
transition is martensitic and have enabled the structures of the austenite and
martensite phases in both compounds to be established. The temperatures
at which the transitions occur in the two alloys are similar, as are the
structures of both their austenite and martensite phases. The austenite phase
of Co1.52Ni1.32Al1.16 is partially ordered in the B2 structure. The martensite
phase in both compounds arises from a simple tetragonal distortion of the cubic
cell. Unlike the related ferromagnetic shape memory compound Ni2MnGa,
the martensitic transitions are not abrupt and there is a temperature range of
at least 100 K in which both tetragonal and cubic phases coexist. The widths
of the cubic Bragg peaks are resolution limited but those associated with the
tetragonal structure showbroadening consistentwith the presence of anisotropic
micro-strain.